This project is aimed at understanding and explaining human thought processes. It seeks to discover how people are able to perform complex tasks and to account for individual differences in the processes used and the success achieved by different persons performing the same tasks. The study of problem-solving and concept formation depends on the development of improved instruments for observing and measuring ongoing cognitive processes. There is a special emphasis on protocol analysis, automatic data recording and analysis, and computer controlled experimentation. As a major technique, the project creates and tests detailed theories of cognitive behavior expressed in the form of computer programs that can be used for computer simulation of human information processing. With these techniques, behavior in problem solving and other language based tasks are analyzed in terms of the underlying processes and mechanisms of perception and memory--thus reducing the complex behaviors to organizations of simpler component processes.